1. Field of the Invention
The present invention relates to an image forming apparatus and a developing device used in the image forming apparatus for copying machines, facsimile machines, printers and other information processing systems, which utilize an electrophotographic process wherein a visual image is produced on a photosensitive member by a developer by use of electrostatic attraction, and the visual image is transferred to a sheet.
2. Discussion of Background
In an image forming apparatus wherein a visual image is produced on a photosensitive member 1a by a developer, such as a toner, and the visual image is transferred onto a material for transfer, such as a sheet, conveyed along a conveyance path M as shown in FIG. 17, a developing unit 2 has a cover 203 provided, with a certain clearance, above a developing roller 3 for causing the developer to adhere to a latent image on the photosensitive member 1a as shown in FIG. 18.
When the rotational direction of the developing roller 3 in the developing unit 2 is set such that the developing roller rotates in a direction against gravity at a contacting point of the developing unit 2 with or a point of the developing unit closest to the photosensitive member 1a, air is introduced into the developing unit 2 through the clearance above the developing roller 3 by rotation of the developing roller 3 as shown in FIG. 18 to increase the air pressure in the developing unit 2, causing the air in the developing unit 2 to be discharged through a gap of the developing unit 2 or lateral gaps at both ends of the developing roller 3. Concomitantly, some part of the developer stored in the developing unit 2 blows out through these gaps, contaminating the interior of the apparatus or scattering the developer.
One of protection measures is that the clearance above the developing roller 3 is eliminated to prevent the inner pressure in the developing unit 2 from increasing. However, when the cover 203 is configured to have a leading edge put into contact with a surface of the photosensitive member 1a, the surface of the photosensitive member 1a is apt to be damaged by the leading edge, which is not desirable.
The present invention is proposed in consideration of the problems and provides an image forming apparatus capable of preventing a developer from scattering from a developing unit by preventing the air pressure in the developing unit from increasing without damaging a surface of a photosensitive member. Another object of the present invention is to provide a developing device capable of preventing a developer stored therein from scattering as well.
In order to attain an object, the present invention adopts an arrangement for regulating a clearance for a surface of a developer carrying member above the developer carrying member as stated later on. The present invention clarifies what extent of the clearance is effective, where a clearance regulated position should be located, to what extent a clearance regulated range is set, and what shape of a clearance regulating portion is preferable.
Specifically, the image forming apparatus according to the present invention is characterized in that the apparatus comprises:
a photosensitive member adapted to have an electrostatic latent image carried thereon;
a developing unit including a developer carrying member rotatable in a direction against gravity at a contacting point with or a point closest to the photosensitive member, and a cover for sealing a developer to be conveyed by the developer carrying member therein, the developer carrying member carrying and conveying the developer stored in the cover to develop the electrostatic latent image on the photosensitive member; and
a clearance regulating member provided so as to be free from contact with a surface of the developer carrying member, the clearance regulating member regulating a clearance for an upper side of the developer carrying member;
wherein the clearance between the developer carrying member and the clearance regulating member is determined at a size not greater than a maximum height of the developer projected from the surface of the developer carrying member.
In accordance with the present invention, the clearance for the surface of the developer carrying member above the developer carrying member can be regulated by the clearance regulating member to restrict supply of air into the developing unit and restrain an increase in the air pressure in the developing unit, thereby preventing the developer from scattering from the developing unit.
The developer carrying member may be configured to be a developing roller, a brush, a belt and so on. The developer carrying member may be configured in any fashion as long as it rotates, carrying the developer thereon.
With respect to the rotational direction of the developer carrying member 3a rotatable in the direction against gravity at the contacting point with or the point closest to, the photosensitive member 1a, there are examples shown in FIGS. 19(a), (b), (c) and (d) with respect of combination of the developer car 3a with the photosensitive member 1a In the case of the developing unit 2 having the developer carrying member 3a rotating in such a rotational direction, the developer is apt to scatter since air is introduced into the developing unit 2 by rotation of the developer carrying member 3a to increase the inner pressure in the developing unit 2 as stated earlier. In the present invention, the clearance regulating member prevents air from being introduced. The inventors have found on experiments stated later that there are significant differences according to the extent in regulation of the clearance, and the inventors have attained the present invention.
The present invention provides not only the arrangement of the image forming apparatus but also the arrangement of a developing device as stated earlier. Specifically, according to one aspect of the invention, the developing device is characterized in that the device comprises a developer carrying member rotatable in a direction against gravity at a contacting point with, or a point closest to, a photosensitive member adapted to have an electrostatic latent image carried thereon, and a cover for sealing a developer to be conveyed by the developer carrying member in the cover, the developer carrying member carrying and conveying the developer stored therein to develop the electrostatic latent image on the photosensitive member; and the device further comprises at least a clearance regulating member provided so as to be free from contact with a surface of the developer carrying member, the clearance regulating member regulating a clearance for an upper side of the developer carrying member; wherein the clearance between the developer carrying member and the clearance regulating member is determined at a size not greater than a maximum height of the developer projected from the surface of the developer carrying member.
When the developer carrying member is configured to have magnetic poles, it is preferable, according to another aspect of the invention, that the clearance for the developer carrying member provided by the clearance regulating member is determined at a size not greater than a height of a magnetic brush of the developer at a magnetic pole just downstream of a clearance regulated position in terms of rotation of the developer carrying member.